Integrated Circuits (ICs) such as memory devices, microprocessors, digital signal processors, application-specific ICs and the like conventionally include one or more voltage regulators for maintaining an internal supply voltage at a constant level despite changing load current conditions within an IC. The regulated supply voltage powers circuitry downstream of the regulator. Powering circuitry with a constant supply voltage enables stable and reliable circuit operation.
A conventional voltage regulator has a closed loop amplifier stage that compares the supply voltage output by the regulator to a reference voltage. Any difference between the two voltages is amplified and used to adjust regulator operation. If the regulated supply voltage decreases, e.g., due to increasing current load, the amplifier stage causes an output stage of the regulator to increase its output voltage. Conversely, if the regulated supply voltage increases, e.g., due to decreasing current load, the regulator output stage decreases its output voltage. As such, the closed loop amplifier stage maintains the regulated supply voltage at approximately a constant voltage level.
However, the closed loop amplifier stage of a voltage regulator produces an inherent voltage drop. The voltage drop is reflected in the amplifier output. That is, the amplifier output is slightly reduced due to the inherent voltage drop. The voltage drop carries through to the output stage of the regulator, thus causing a slight voltage reduction in the regulated voltage output.
Regulator-induced voltage drop may adversely affect downstream circuit operation. For example, circuit performance is degraded when the regulated voltage supplying the circuit falls below a critical level, the critical level being the voltage at which the circuit begins to behave unexpectedly or unreliably. Circuit operation is unaffected by a reduction in supply voltage so long as the supply voltage remains above the critical level. However, for low voltage applications, regulator-induced voltage drop may cause the regulated supply voltage to drop below the critical level, causing undesired circuit operation. As such, IC performance is hindered during low voltage operation by powering internal circuitry with a regulated supply voltage.